1. Field of the Invention
The present invention relates to a process for forming, on the surface of a resin molded product, a metal layer which is useful for forming a metal film. More particularly, the present invention relates to a process for forming, on the surface of a resin molded product, a metal layer of a fine metal powder produced by bringing a metal powder producing material into flowing contact with the surface of the resin molded product in a treating vessel.
2. Description of the Related Art
For the purpose of providing, to a resin molded product, various properties such as an ornamentality, a weather resistance, a surface electrical conductivity, an electromagnetic wave shielding property, an antibacterial property and the like, it is a conventional practice to form a metal film on the surface of the resin molded product. Examples of conventionally known processes for forming a metal film are a vacuum plating process such as a vacuum deposition and a sputtering, an electroless plating process, an electroless plating/electroplating process comprising an electroless plating step and an electroplating step, and the like. These processes have been put into practical use in various fields, because an electroplating process cannot be applied directly to the resin molded product due to the non-electrical conductivity of the resin molded product.
However, the vacuum plating process suffers from problems that a metal film formed by this process has a lower peel strength and a poor durability, that it is difficult to apply this process to a molded product having a complicated shape, that a long time is required for the vacuum processing, because a gas may be generated depending on the type of a resin, and that a production cost is higher.
The electroless plating process suffers from the following problems: It is usually necessary to previously subject the surface of a resin molded product to an etching, or to subject the surface to a catalytic effect providing process such as a sensitizing/activating process. For this reason, the steps are complicated; a long time is required for the processing; and a plated film produced has a small thickness.
In the electroless plating/electroplating process, a metal film formed by this process has a relatively good peel strength, and a durability which is remarkably good, as compared with that of a metal film formed by the vacuum plating process. However, the electroless plating/electroplating process suffers from problems that the steps are complicated, and that a long time is required for the processing.
There is also a proposed metal film forming process comprising a step of applying a resin including a metal powder added thereto to the surface of a resin molded product to provide an electrical conductivity to the surface of it, and an electroplating step. However, this process suffers from a problem that it is generally difficult to provide a resin layer uniformly on the surface of a resin molded product and for this reason, it is impossible due to the ununiformity of the resin layer to form a metal film excellent in thickness accuracy and in surface smoothness.